The Sanfilippo syndrome type B is a neurodegenerative disorder caused by deficiency of the lysosomal enzyme, alpha-N- acetylglucosaminidase and the resulting failure to degrade heparan sulfate. It is characterized by profound mental retardation and behavioral disturbances in childhood, accompanied by relatively mild somatic manifestations; dealth usually occurs in the late teens. We have cloned and characterized the gene (NAGLU) and cDNA encoding alpha-N-acetylglucosaminidase and identified over a dozen mutations in cells from patients with Sanfilippo B syndrome. The overall goal of this project is to increase understanding of the disease. Aim 1 is to complete the study of normal and mutant NAGLU genes, to characterize the normal and mutant enzymes, and to prepare recombinant enzyme and antisera. Aim 2 is to generate a mouse model of the disease by homologous recombination, and to characterize the mutant mouse at the biochemical, pathological and clinical level, with particular emphasis on the effect of the disease on the brain. Aim 3 is to use the mouse model in order to test the therapeutic value of administering alpha-N-acetylglucosaminidase either directly, or indirectly through genetically engineered cells. For the latter, a deficient mouse will be engineered, in which only cells of the macrophage lineage (including microglia in the brain) would express the NAGLU gene. Enzyme uptake and correction of pathology will be monitored. Aim 4 is to understand the loss of mRNA associated with mutations that lead to premature translation termination, a puzzling phenomenon observed in numerous genetic disorders. Using the common Tay-Sachs mutation in stably transfected cells as a model system, we will pursue our current results, which implicate translation as the step at which the mutant mRNA is targeted for degradation. Structural elements in mRNA required for this degradation will be sought. Applicability of findings to premature stop mutations in other diseases, including the Sanfilippo B syndrome, will be sought.